Esterification catalyst, polyester process and polyester article

ABSTRACT

A catalyst composition for producing polyesters comprises: a) an organometallic compound obtained by reacting an orthoester or condensed orthoester of titanium, zirconium or aluminum, an alcohol containing at least two hydroxyl groups, a 2-hydroxy carboxylic acid and a base; and b) at least one compound comprising germanium, antimony or tin. Polyesters obtained by esterification reaction in the presence of the catalyst compositions according to the present invention exhibit improved melt properties and are particularly suitable for production of textile and commercial fibers, films and rigid packaging.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Phase of International Application No.PCT/US01/43256, filed Nov. 21, 2001, and which further claims priorityfrom U.S. Provisional Application No. 60/252,079, filed Nov. 21, 2000.These applications, in their entirety, are incorporated herein byreference.

BACKGROUND OF THE INVENTION

The invention concerns a polyester fibre composition and a process forits manufacture which utilises a novel organotitanium or organozirconiumcatalyst

Antimony (Sb), tetraisopropyl titanate, and triethanolamine titanate areknown catalysts for esterification processes. Also, organotitaniumcompounds and, in particular, titanium alkoxides or orthoesters areknown as catalysts for esterification processes. Many organotitaniumcompounds which are effective catalysts in the manufacture of polyesterssuch as polyethylene terephthalate are known to produce unacceptableyellowing in the final polymer. U.S. Pat. No. 5,866,710 describes anesterification process using a catalyst system which comprises thereaction product of an orthoester or condensed orthoester of titanium orzirconium, an alcohol containing at least two hydroxyl groups, a2-hydroxy carboxylic acid and a base. The polyesters produced by such aprocess show a reduced amount of haze and yellowing in comparison to aknown titanium isopropoxide catalyst U.S. Pat. No. 5,866,710 teachesthat the resulting polyesters are useful in films and bottles; thereference does not teach or suggest using the resulting polyesters infiber or yarn.

When polyester articles are formed from molten polyester, whenprocessing polyesters into textile fibres or bottles for example, thepolymer is melted and may be held in the molten state for a period oftime before being shaped by e.g. spinning or injection moulding. Two keyrheology measurements: shear viscosity or complex viscosity as afunction of shear rate or frequency and extensional viscosity as afunction of shear stress are used to characterize polyesters. Zero-shearviscosity is typically taken as an indication of polymer molecularweight while the transient extensional viscosity is an indicator of thepolymer's extensional response to stretching.

We have now found a catalyst composition for producing polyesters inparticular which exhibit unexpectedly improved melt rheologicalproperties compared with polyester of the same intrinsic viscosity madeusing known catalyst systems, and which are therefore particularlysuitable for making polyesters for such applications.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved processfor preparing polyesters and an improved organometallic composition foruse as a catalyst in such processes. It is also an object of the presentinvention to provide an improved polyester for melt processingapplications and also formed articles made from the improved polyester.

According to the invention we provide a catalyst composition suitablefor use as a catalyst for the preparation of an ester comprising:

(a) an organometallic compound which is the reaction product of anorthoester or condensed orthoester of titanium, zirconium or aluminium,an alcohol containing at least two hydroxyl groups, a 2-hydroxycarboxylic acid and a base, and

(b) at least one compound of germanium, antimony or tin.

According to a second aspect of the invention, we provide a process forthe preparation of a polyester which comprises carrying out apolyesterification reaction in the presence of a catalyst, whichcatalyst comprises (a) an organometallic compound which is the reactionproduct of an orthoester or condensed orthoester of titanium, zirconiumor aluminium, an alcohol containing at least two hydroxyl groups, a2-hydroxy carboxylic acid and a base, and (b) at least one compound ofgermanium, antimony or tin.

According to a third aspect of the invention, we provide a polyesterarticle made by a process which comprises carrying out apolyesterification reaction in the presence of a catalyst, whichcatalyst comprises:

(a) an organometallic compound which is the reaction product of anorthoester or condensed orthoester of titanium, zirconium or aluminium,an alcohol containing at least two hydroxyl groups, a 2-hydroxycarboxylic acid and a base, and

(b) at least one compound of germanium, antimony or tin to form apolyester material having an intrinsic viscosity of at least 0.5 dl/g,as measured by capillary viscometry using the method of ASTM D-4603, andsubsequently forming the polyester article from the polyester materialin the molten phase.

According to a fourth aspect of the invention, we provide a polyesterarticle containing residues of a catalyst system which comprises (a) thereaction product of an orthoester or a condensed orthoester of titanium,zirconium or aluminium, an alcohol containing at least two hydroxylgroups, a 2-hydroxy carboxylic acid and a base and (b) at least onecompound of germanium, antimony or tin.

The present invention also provides an unexpected result, that is atitanium based catalyst system having improved extensional viscositycompared with prior art tetraisopropyl titanate. This result isparticularly beneficial in making polyester for fiber spinningapplications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 show rheological properties for polyester made from aprior art antimony catalyst and a titanium catalyst

FIGS. 3 and 4 show rheological properties for polyester made from thecatalysts of the invention and a prior art comparison.

FIG. 5 shows a measure of crystallinity and orientation index forpolyester fibres of the invention and an antimony comparison.

DETAILED DESCRIPTION OF THE INVENTION

The organometallic compound suitable for use in an esterificationprocess as component (a) of the aforementioned catalyst compositioncomprises the reaction product of an orthoester or condensed orthoesterof at least one metal selected from titanium, zirconium or aluminium.Normally an orthoester or condensed orthoester of one of the selectedmetals is used but it is within the scope of the invention to use anorthoester or condensed orthoester of more than one of the selectedmetals. For clarity we refer hereinafter to a titanium, zirconium oraluminium orthoester or condensed orthoester, and all such referencesshould be taken to include orthoesters or condensed orthoesters of morethan one metal, e.g. to a mixture of titanium and zirconium orthoesters.

Preferably, the orthoester has the formula M(OR)₄ or Al(OR)₃ where M istitanium or zirconium and R is an alkyl group. More preferably Rcontains 1 to 6 carbon atoms and particularly suitable orthoestersinclude tetraisopropoxy titanium, tetra-n-butoxy titanium,tetra-n-propoxy zirconium, tetra-n-butoxy zirconium and tri-iso-butoxyaluminium.

The condensed orthoesters suitable for preparing the organometalliccompounds used in this invention are typically prepared by carefulhydrolysis of titanium, zirconium or aluminium orthoesters. Titanium orzirconium condensed orthoesters are frequently represented by theformulaR₁O[M(OR₁)₂O]nR₁in which R¹ represents an alkyl group and M represents titanium orzirconium. Preferably, n is less than 20 and more preferably is lessthan 10. Preferably, R¹ contains 1 to 12 carbon atoms, more preferably,R¹ contains 1 to 6 carbon atoms and useful condensed orthoesters includethe compounds known as polybutyl titan ate, polyisopropyl titanate andpolybutyl zirconate.

Preferably the alcohol containing at least two hydroxyl groups is adihydric alcohol and can be a 1,2-diol such as 1,2-ethanediol,1,2-propanediol, a 1,3-diol such as 1,3-propanediol or a dihydricalcohol containing a longer chain such as diethylene glycol or apolyethylene glycol. Preferred dihydric alcohols are 1,2-ethanediol anddiethylene glycol. The organometallic compound can also be prepared froma polyhydric alcohol such as glycerol, trimethylolpropane orpentaerythritol.

Preferably the organometallic compound is prepared by reacting adihydric alcohol with an orthoester or condensed orthoester in a ratioof from 2 to 12 moles of dihydric alcohol to each mole of the titaniumor zirconium. More preferably the reaction product contains 4 to 8 molesdihydric alcohol per mole of titanium, zirconium or aluminium.

Preferred 2-hydroxy-carboxylic acids include lactic acid, citric acid,malic acid and tartaric acid. Some suitable acids are supplied ashydrates or as aqueous mixtures. Acids in this form as well as anhydrousacids are suitable for preparing the catalysts used in this invention.The preferred molar ratio of acid to titanium or zirconium in thereaction product is 1 to 4 moles per mole of titanium or zirconium. Morepreferably the organometallic compound contains 1.5 to 3.5 moles of2-hydroxy acid per mole of titanium or zirconium.

A base is also used in preparing the reaction product which is used asthe organometallic compound in the catalyst of the invention. The basemay be an inorganic base or an organic base but is generally aninorganic base and suitable bases include sodium hydroxide, potassiumhydroxide, ammonium hydroxide, sodium carbonate, magnesium hydroxide andammonia. Preferred organic bases include quaternary ammonium compoundssuch as tetrabutyl ammonium hydroxide, tetraethylammonium hydroxide,choline hydroxide, (trimethyl (2-hydroxyethyl)ammonium hydroxide) orbenzyltrimethyl ammonium hydroxide, or alkanolamines such asmonoethanolamine, diethanolamine, triethanolamine andtriisopropanolamine. Usually, the amount of base used is in the range0.1 to 12 mole base per mole of metal (titanium, zirconium oraluminium). The preferred amount is in the range 0.1 to 4.0 mole baseper mole of titanium, zirconium or aluminium.

Frequently, the amount of base used is sufficient to fully neutralisethe 2-hydroxy carboxylic acid but it is not essential that the acid isfully neutralised.

In one preferred embodiment the organometallic compound comprises thereaction product of a titanium orthoester, citric acid, a dihydricalcohol and an inorganic base in which the mole ratio oftitanium:acid:dihydric alcohol:base is in the range 1:1.5-3.5:4-10:2-12.

Typically, the organometallic compound is neutral. It is frequentlyconvenient to add water together with the base when preparing thecatalysts. Frequently, products which contain water have a pH in therange 6 to 8.

The organometallic compound can be prepared by mixing the components(orthoester or condensed orthoester, dihydric alcohol, 2-hydroxy acidand base) with removal of any by-product, (e.g. isopropyl alcohol whenthe orthoester is tetraisopropoxytitanium), at any appropriate stage. Inone preferred method the orthoester or condensed orthoester and dihydricalcohol are mixed and subsequently, 2-hydroxy acid and then base areadded or a pre-neutralised 2-hydroxy acid solution, is added. In analternative preferred method the orthoester or condensed orthoester isreacted with the 2-hydroxy acid and by-product alcohol is removed. Baseis then added to this reaction product followed by a dihydric alcohol toproduce the reaction product which is used in the catalyst of theinvention. If desired, further by-product alcohol can then be removed bydistillation. U.S. Pat. No. 5,866,710 is incorporated herein byreference.

Component (a) alone may be used as the catalyst to make polyester forfibre applications including textile fiber and industrial fiber. Theterm “industrial fiber” as used herein includes fibre useful in themanufacture of tire cord, broad wovens, seat belts, conveyor belts, Vbelts, air bags, cut resistant articles, and ropes. Industrial fiber maybe made by known methods such as those disclosed in U.S. Pat. Nos.5,085,818; 5,132,067; 5,397,527; 5,630,976; 5,830,811; and 6,071,835;these patents are incorporated herein by reference.

Component (b) of the catalyst composition of the invention is a compoundof germanium, antimony or tin and, in general, any compound can be usedincluding mixtures of compounds of more than one of these metals. Thepreferred compound of germanium is germanium dioxide. Preferably, theantimony compound is antimony trioxide or a salt of antimony, forexample antimony triacetate. A number of tin compounds are suitable,including salts, such as tin acetate and organotin compounds, such asdialkyl tin oxides, for example, dibutyl tin oxide, dialkyl tindialkanoates, for example, dibutyl tin dilaurate and alkylstannoicacids, for example butylstannoic acid (C₄H₉SnOOH).

A wide range of proportions of components (a) and (b) can be present inthe catalyst composition of the invention. Generally, the weight ratioof component (a) to component (b) is in the range 1:0-1000, calculatedas weight of Ti, Zr or Al to weight of Ge, Sb or Sn. The two components,(a) and (b) may be premixed to form the catalyst composition of thisinvention before the composition is mixed with the reactants for anesterification reaction. Alternatively, components (a) and (b) can beseparately added to the reactants in order to carry out anesterification reaction according to this invention.

The esterification reaction of the process of the invention can be anyreaction by which an ester is produced. The reaction may be (i) a directesterification in which a carboxylic acid or its anhydride and analcohol react to form an ester or (ii) a transesterification(alcoholysis) in which a first alcohol reacts with a first ester toproduce an ester of the first alcohol and a second alcohol produced bycleavage of the first ester or (iii) a transesterification reaction inwhich two esters are reacted to form two different esters by exchange ofalkoxy radicals. Direct esterification or transesterification can beused in the production of polymeric esters and a preferred process ofthe invention comprises a polyesterification process. Many carboxylicacids and anhydrides can be used in direct esterification includingsaturated and unsaturated monocarboxylic acids and anhydrides of suchacids such as stearic acid, isostearic acid, capric acid, caproic acid,palmitic acid, oleic acid, palmitoleic acid, triacontanoic acid, benzoicacid, methyl benzoic acid, salicylic acid and rosin acids such asabietic acid, dicarboxylic acids such as phthalic acid, isophthalicacid, terephthalic acid, sebacic acid, adipic acid, azelaic acid,succinic acid, fumaric acid, maleic acid, naphthalene dicarboxylic acidand pamoic acid and anhydrides of these acids and polycarboxylic acidssuch as trimellitic acid, citric acid, trimesic acid, pyromellitic acidand anhydrides of these acids. Alcohols frequently used for directesterification include aliphatic straight chain and branched monohydricalcohols such as butyl, pentyl, hexyl, octyl and stearyl alcohols,dihydric alcohols such as 1,2-ethanediol, 1,3-propanediol,1,4-butanediol and 1,6 cyclohexane dimethanol and polyhydric alcoholssuch as glycerol and pentaerythritol.

The esters employed in an alcoholysis reaction are generally the lowerhomologues such as methyl, ethyl and propyl esters since, during theesterification reaction, it is usual to eliminate the displaced alcoholby distillation. These lower homologue esters of the acids suitable fordirect esterification are suitable for use in the transesterificationprocess according to the invention. Frequently (meth)acrylate esters oflonger chain alcohols are produced by alcoholysis of esters such asmethyl acrylate, methyl methacrylate, ethyl acrylate and ethylmethacrylate. Typical alcohols used in alcoholysis reactions includebutyl, hexyl, n-octyl and 2-ethyl hexyl alcohols and substitutedalcohols such as dimethylaminoethanol.

When the esterification reaction is a transesterification between twoesters, generally the esters will be selected so as to produce avolatile product ester which can be removed by distillation.

In direct esterification the acid or anhydride and an excess of alcoholare typically heated, if necessary in a solvent, in the presence of thecatalyst composition. Water is a by-product of the reaction and this isremoved, as an azeotrope with a boiling mixture of solvent and/oralcohol. Generally, the solvent and/or alcohol mixture which iscondensed is at least partially immiscible with water which is thereforeseparated before solvent and/or alcohol are returned to the reactionvessel. When reaction is complete the excess alcohol and, when used,solvent are evaporated. In view of the fact that the catalystcompositions of the invention do not normally form insoluble species, itis not generally necessary to remove them from the reaction mixture, asis frequently necessary with conventional catalysts. A typical directesterification reaction is the preparation of bis(2-ethylhexyl)phthalate which is prepared by mixing phthalic anhydride and 2-ethylhexanol. An initial reaction to form a monoester is fast, but thesubsequent conversion of the monoester to diester is carried out byrefluxing in the presence of the catalyst composition at a temperatureof 180-200° C. until all the water has been removed. Subsequently theexcess alcohol is removed.

In an alcoholysis reaction, the ester, first alcohol and catalystcomposition are mixed and, generally, the product alcohol (secondalcohol) is removed by distillation, often as an azeotrope with theester. Frequently it is necessary to fractionate the vapour mixtureproduced from the alcoholysis in order to ensure that the second alcoholis separated effectively without significant loss of product ester orfirst alcohol. The conditions under which alcoholysis reactions arecarried out depend principally upon the components of the reaction andgenerally components are heated to the boiling point of the mixtureused.

A particularly preferred embodiment of the esterification process of theinvention is a polyesterification reaction in the presence of thecatalyst composition of the invention. Polyesters can be produced byprocesses involving direct esterification or transesterification. In apolyesterification reaction polybasic acids or esters of polybasic acidsare usually reacted with polyhydric alcohols. Preferred reactants aredicarboxylic acids such as phthalic acid, isophthalic acid, terephthalicacid, sebacic acid, adipic acid, azelaic acid, succinic acid, fumaricacid, maleic acid, naphthalene dicarboxylic acid and pamoic acid andesters and anhydrides of these acids and polycarboxylic acids such astrimellitic acid, citric acid, trimesic acid, pyromellitic acid andesters and anhydrides of these acids. Preferred alcohols includealiphatic straight chain and branched polyhydric alcohols such as1,2-ethanediol (ethylene glycol), 1,4-butanediol (butylene glycol),1,3-propanediol, 1,6-hexanediol, cyclohexane dimethanol,trimethylpropane, glycerol and pentaerythritol.

Preferred polyesterification reactions according to the inventioninclude the reaction of terephthalic acid or dimethyl terephthalate with1,2-ethanediol (ethylene glycol) to produce polyethylene terephthalateor with 1,4-butanediol (butylene glycol) to produce polybutyleneterephthalate or reaction of naphthalene dicarboxylic acid with1,2-ethanediol to produce polyethylene naphthalenate. Other glycols suchas 1,3-propanediol, 1,6- hexanediol, trimethylpropane andpentaerythritol are also suitable for preparing polyesters.

The esterification reaction of the invention can be carried out usingany appropriate, known technique for an esterification reaction.

A typical process for the preparation of polyethylene terephthalatecomprises two stages. In the first stage terephthalic acid or dimethylterephthalate is reacted with 1,2-ethanediol to form a prepolymer andthe by-product water or methanol is removed. The prepolymer issubsequently heated in a second stage to remove 1,2-ethanediol and forma long chain polymer. Either or both these stages may comprise anesterification process according to this invention.

A typical batch production of polyethylene terephthalate is carried outby charging terephthalic acid and ethylene glycol to a reactor alongwith catalyst composition, if desired, and heating the contents to260-270° C. under a pressure of about 0.3 MPa. Reaction commences as theacid dissolves at about 230° C. and water is removed. The product istransferred to a second autoclave reactor and catalyst composition isadded, if needed. The reactor is heated to 285-310° C. under an eventualvacuum of 100 Pa to remove ethylene glycol by-product. The moltenproduct ester is discharged from the reactor, cooled and chipped. Thechipped polyester may be then subjected to solid state polymerisation,if appropriate.

A preferred means of adding the catalyst compositions of this inventionto a polyesterification reaction is in the form of a slurry in theglycol being used (e.g. ethylene glycol in the preparation ofpolyethylene terephthalate). Components (a) and (b) can be added to thereaction mixture as separate slurries or mixed to prepare a slurrycontaining both components, which slurry is then added to the reactants.This method of addition is applicable to addition of the catalystcomposition to the polyesterification reaction at the first stage or atthe second stage.

The amount of catalyst used in the esterification process of theinvention generally depends upon the total metal content (expressed asamount of Ti, Zr or Al plus amount of Ge, Sb or Sn) of the catalystcomposition. Usually the amount is from 0.2 to 1200 parts per million(ppm) of metal based on weight of product ester for direct ortransesterification reactions. Preferably, the amount is from 5 to 500ppm of total metal based on weight of product ester: Inpolyesterification reactions the amount used is generally expressed as aproportion of the weight of product polyester and is usually from 5 to500 ppm expressed as total metal (Ti, Zr or Al plus Ge, Sb or Sn) basedon product polyester.

Generally, the amount of Ti, Zr or Al used in a direct esterification ortransesterification will be in the range 0.1 to 50 ppm Ti, Zr or Al andmore preferably in the range 0.1 to 30 ppm Ti, Zr or Al, based onproduct ester; and the amount of Ge, Sb or Sn used in a directesterification or transesterification will be in the range 5 to 700 ppmGe, Sb or Sn, preferably in the range 5 to 400 ppm Ge, Sb or Sn, basedon product ester. For polyesterification, the preferred amount of Ti, Zror Al is in the range 0.2 to 50 ppm Ti, Zr or Al based on productpolyester. The preferred amount of Ge, Sb or Sn used inpolyesterification is in the range 5 to 500 ppm Ge, Sb or Sn.

Additional compounds may be added to the polyesterification reaction ifrequired. It is common to add a polymer stabiliser to the reactionmixture to stabilise the polymer against thermal degradation. A commonstabiliser comprises a phosphorus compound, e.g. phosphoric acid. Colouradjustment compounds may also be added at this stage. For example,cobalt compounds, e.g. cobalt acetate, or organic dyes may be added tofurther counteract any tendency towards yellowness in the final polymer.For textile fibres, dyes, optical brighteners, pigments or dyepretreatments may be added to enhance dye retention or improve thesusceptibility of the polymer to dyeing. It may also be required tocontrol the co-products of the polyesterification process, in particularthe diethylene glycol (DEG) content of the polymer, by addition of DEGsuppressants such as bases or amines, as is known in the art. The DEGcontent of the polymer is believed to affect the thermal properties ofthe polymer. For certain applications, the DEG content should be lowalthough for textile fibre it may be desirable to control the level ofDEG to 0.8-1.5 weight %

The inventive catalyst combination comprising compound (a) and compound(b) may be used to make polyester for fiber applications includingtextile fiber and industrial fiber; moulding applications, includingstretch blow moulding for e.g. rigid packaging such as bottles, jars andclamshell packs, extrusion for e.g. film, including oriented polyesterfilm, and flexible packaging. The fiber may be made according to knownmethods cited above.

The invention is illustrated by the following examples.

EXAMPLE 1

Preparation of Compound A

Citric acid monohydrate (132.5 g, 0.63 moles) was dissolved in water(92.8 g). To the stirred solution was slowly added titanium isopropoxide(72.0 g, 0.25 moles). This mixture was heated to reflux for 1 hour toyield a hazy solution. This solution stripped under vacuum to removefree water and isopropanol. The product was cooled below 70° C. and 32%w/w aqueous sodium hydroxide (94.9 g, 0.76 moles) was added slowly tothe stirred solution. The product was filtered, mixed with ethyleneglycol (125.5 g, 2.0 moles) and heated under vacuum to remove freewater/isopropanol. The product was a slightly hazy, very pale yellowliquid (Ti content 3.85% by weight), which is referred to hereinafter asCompound A

Preparation of Compound B

Ethylene glycol (217.85 g, 3.51 moles) was added from a dropping funnelto stirred titanium isopropoxide (284.8, 1.00 mole) in a 1 literfishbowl flask fitted with stirrer, condenser, and thermometer. The rateof addition was controlled so that the heat of reaction caused thecontents of the flask to warm to about 50° C. The reaction mixture wasstirred for 15 minutes and aqueous 85% wt/wt ammonium lactate (251.98 g,2.00 moles) was added to the reaction flask to yield a clear, paleyellow liquid (Ti content 6.54% by weight).

Preparation of Compound C

Following the method for Compound B, ethylene glycol (496.37 g, 8.0moles) was added to titanium isopropoxide (284.8 g, 1.0 mole) followedby reaction with aqueous 60% wt/wt sodium lactate (374.48 g, 2.0 moles)to yield a pale yellow liquid (Ti content 4.13% by weight).

Preparation of Compound D

To titanium isopropoxide (142.50 g. 0.50 mole) in a one liter conicalflask, fitted with sidearm condenser, supported on and stirred by meansof a magnetic stirrer was slowly added ethylene glycol (248.25 g, 4.0moles) from a dropping funnel. When addition was complete, the contentswere stirred for 15 minutes before adding aqueous 60% wt/wt potassiumlactate (213.03 g, 1.0 mole) by dropping funnel to yield a clear, verypale yellow product (Ti content 3.91% by weight).

Preparation of Compound E

Following the method for Compound D, diethylene glycol (127.58 g, 1.20moles) was added to 135.95 g (0.3 mole) zirconium n-propoxide (72.3%wt/wt in n-propanol). To this stirred product was added aqueous 60% w/wtsodium lactate (112.04 g, 0.60 mole) to yield a pale yellow product (Zrcontent 7.28% by weight).

EXAMPLE 2

Preparation of Polymer 1

Compound A, prepared in Example 1 was used to prepare polyethyleneterephthalate (PET) in the following way. Ethylene glycol (930 litres)and terephthalic acid (2250 kg) were charged to a stirred jacketedreactor. The catalyst and other additives were added and the reactorheated to 226-252° C. at a pressure of 2.9 bar to initiate the firststage direct esterification (DE) process. On completion of the DEreaction, (i.e. when water production stopped, indicated by a rise incolumn temperature), the contents of the reactor were allowed to reachatmospheric pressure before a vacuum was steadily applied. Sodiumhydroxide (100 ppm) was added as a diethylene glycol suppressant and themixture heated to 294±2° C. under vacuum to remove ethylene glycol andyield polyethylene terephthalate. The final polyester was dischargedonce a constant torque had been reached which indicated an intrinsicviscosity (IV) of around 0.62. The chipped polymer was then subjected tosolid state polymerisation at about 230° C. in flowing nitrogen toincrease the polymer molecular weight so as to have an intrinsicviscosity of about 1.0.

Polyesters of the invention were made using:

-   -   as catalyst compositions,        -   Compound A plus antimony trioxide (at 5 ppm Ti+250 ppm Sb)            (i.e. a catalyst composition according to the invention)        -   Compound A alone (15 ppm),    -   and as comparisons:        -   antimony trioxide alone (350 ppm)        -   tetra(isopropoxy)titanium (15 ppm) (VERTEC™ TIPT™ available            from ICI Synetix).            Properties of the Polymer Samples.            Intrinsic Viscosity (IV)

The polymer intrinsic viscosities were measured by glass capillaryviscometry using 60/40 phenol/1,2,2-tetrachlorethane as solvent at 25°C.

Thermal Characteristics by DSC Analysis

Heat-cool differential scanning calorimetry (DSC) experiments on‘re-quenched’ samples were conducted as follows: 10 mg samples weredried at 80° C. in a vacuum oven. These dried samples were then held at290° C. for 2 minutes in a Perkin-Elmer DSC instrument, before beingquenched onto the cold block (−40° C.). The re-quenched samples werethen subjected to a heat/hold 2 minutes/cool procedure, at heating &cooling rates of 20° C./minute on a Perkin-Elmer DSC 7a. The coolingdata quoted below have been corrected by adding 2.8° C. to thecomputer-generated temperatures. The results are shown in Table 1.

TABLE 1 Metal content IV Tg_(o) Tn_(o) Tn Tp Tc Tc_(o) Catalyst (ppm)(dl/g) (° C.) (° C.) (° C.) (° C.) (° C.) (° C.) Compound 5 + 250 0.9580.0 129.2 149.5 257.1 189.4 201.5 A + Sb2O3 Sb oxide 350 0.99 82.1132.6 155.4 255.9 181.6 194.2 Compound  15 1.03 83.5 na 145.9 258.5188.3 198.4 A TIPT  14 0.99 77 158 180 248 — — KEY: Tg_(o) = polymerglass transition temperature, Tn_(o) = onset of crystallisation(heating), Tn = crystallisation peak (heating), Tc_(o) = onset ofcrystallisation (cooling), Tc = crystallisation (cooling), Tp = peak(melting) temperature.Rotational Rheometry—Dynamic Oscillation

The materials were characterised using a Rheometrics rheometer.

The sample was placed in the rheometer between two 40 mm diameterparallel plates and heated to the measurement temperature 285° C. Thesample was squeezed to remove any voids until a gap of between 1 and 2mm was reached. Any residual material at the edges was removed.

From the measured torque response an in-phase storage modulus G′, and anout of phase loss modulus G″, have been calculated. A complex viscosity,ETA*, has subsequently been calculated from the moduli.

For measurements taken in the linear viscoelastic region (strainindependent) it is possible to equate frequency with shear rate andcomplex viscosity with apparent shear viscosity. Therefore for simpleunfilled systems it is acceptable to think of frequency (rads/s) asshear rate (/s) and complex viscosity (Pa.s) as shear viscosity (Pa.s).

Capillary Rheometry

The materials were characterised at 285° C. using a Rosand capillaryrheometer. The polymer charge was melted in the heated rheometer barrelprior to extrusion. The melt was extruded at a range of flow ratesthrough a die 1 mm in diameter and the pressure drop was measured at thedie entry at each rate. Two parallel measurements using different dielengths were made to allow a die entry correction (Bagley) to be made.The apparent shear and elongational viscosity's (Cogswell) werecalculated from the die geometry and pressure drops recorded. Units ofviscosity are Pa.s. Shear rate is a function of the volumetric flow rateand die geometry and is measured in reciprocal seconds (s⁻¹).

The results in FIG. 4 show that the polymer in which the inventivecatalyst of Compound A is present has extensional viscositysignificantly better than that of polymer made with Sb alone. Thisresult is surprising, given that polyesters made using the prior arttitanium catalyst (titanium tetraisopropoxide) had extensionalviscosities significantly reduced from those of polymers made with Sbcatalysts. Polymer molecular weight may be estimated from the zero shearviscosity measurement, which is typically inferred from the complexviscosity at low frequency of oscillation using rotational rheometry.Normally this means that the extensional viscosity correlates with themolecular weight of the polymer, e.g. a polymer with low zero-shearviscosity typically has a low extensional viscosity. FIG. 3 shows thatpolyester made from Sb alone has a higher zero shear viscosity than theinventive combination of Sb and Compound A Based on the prior arttitanium data in FIGS. 1 and 2, one skilled in the art would haveexpected that the inventive catalyst combination would exhibit a lowerextension viscosity. However, transient extensional viscosities (FIG. 4)are essentially identical for polyester made from the Sb control and theinventive catalyst combination. Thus, the present invention haseliminated the large deficiency in reduced extensional viscosity thatoccurred in polyesters made from prior art titanium catalysts.

We tried using polyester made from titanium tetraisopropoxide catalystto make dimensionally stable polyester yarn according to U.S. Pat. No.5,132,067. With the TIPT polyester, ft appeared possible to achievehigher strength at low dimensional stability or higher dimensionalstability at low strength but not both together as was possible withpolyester made from Sb catalyst The differences in Theologicalcharacterization discussed above are consistent with, and appear toexplain the differences in undrawn response of the two polyesters. Witha significantly lower extensional viscosity, the TIPT polyester has arelatively lower resistance to being stretched and hence in makingindustrial fiber from the polyester, more spinline stress, i.e. higherspinning speed, is required in order to produce the same orientation,e.g., birefringence and crystallinity, in the undrawn industrial fiber.

The behaviour of polyester under stretching flow (elongation) wouldnormally be proportional to the molecular weight of the polyester. Thecatalyst system of the invention, despite the lower molecular weight,demonstrates equivalent or better resistance to stretch flow. This isconsistent with the catalyst system of the invention giving higherspinline stress and ultimately fibre crystallinity.

Chemical Analysis of Polymers

The carboxyl end groups were determined by automatic potentiometrictitration whereby the sample is dissolved in a solvent mixture of 70%o-cresol/30% chloroform and titrated on an autotitrator withstandardized KOH in methanol The polymers were examined by ¹H NMRspectroscopy to determine the amount of diethylene glycol (DEG) residuespresent in the polymer chain (expressed as weight percent of polymer),the proportion of hydroxyl (OH) end groups present (expressed as numberof end groups per 100 polymer repeating units) and the proportion ofvinyl end groups (VEG) present (expressed as number of end groups per100 polymer repeating units).

EXAMPLE 3

Preparation of Fibre

Dried PET chip was fed under nitrogen into a single screw extruderfitted with gear pump, spin block, spin pot and spinnerette. Thetemperature profile of this system was chosen to give the desiredpolymer melt viscosity. A continuous multi-filament product was producedby passing the molten filaments exiting the spinnerette through a heatedsleeve and quench stack and then drawn between heated godet rolls toproduce a product with the desired draw ratio and total denier. Themulti-filament product was collected on cardboard sleeves using anautomatic doff winder and tested off-line.

Fibre Properties

The properties of the fibres made with the three catalyst systems areshown in Table 2. The fibre made from the TIPT-catalysed polymer showedpoor take-up properties and a high rate of fibre breakage compared withfibres made from the other catalysts. For this reason, detailedmeasurements were not made.

The IV loss was measured as the difference between the IV of the chipbefore extrusion and the IV of freefall fibre. The freefall fibre isfibre allowed to fall freely from the spinneret Carboxyl (COOH) valueswere also determined on the freefall fibre. The fray count is measuredby a detector above the take-up winder on fibre spinning. This detectorconsists of a light-beam which measures loops/broken filament within thefibre.

TABLE 2 Compound A + Property Sb₂O₃ Sb₂O₃ Compound A Freefall IV (g/dL)0.85 0.83 0.88 Extrusion IV Loss 0.10 0.16 0.15 COOH 22.5 30.6 20.9Frays/lb 9.8 49.3

The density of the undrawn and drawn yarn is a convenient measure ofpercent crystallinity. Densities of undrawn and drawn yarns weredetermined in n-heptane/carbon tetrachloride density gradient column at23° C. The gradient column was prepared and calibrated according to ASTMD1505-68 with density ranging from 1.30-1.43 g/cm³. Percentagecrystallinity was then calculated from:

${{Weight}\mspace{14mu}\%\mspace{14mu}{XTAL}} = {\frac{\left( {{Ys} - {Ya}} \right)\mspace{11mu}\left( {{Yc}/{Ys}} \right)}{\left( {{Yc} - {Ya}} \right)} \times 100}$

-   Ys—measured density of sample in gm/cm3-   Ya—theoretical density of 100% amorphous phase (1.335 gm/cm³)-   Yc—theoretical density of 100% crystalline phase (1.455 gm/cm³)

The crystallinity and orientation index was determined at variousspinning speeds and is shown graphically in FIG. 5. Although quiescentcrystallisation, e.g. by DSC techniques does not always accuratelyreflect spin-line crystallisation kinetics, however as shown in FIG. 5,for a given fibre orientation index, the percent crystallinity is, innearly all cases, higher for polymers containing the mixed catalystsystem of the invention compared to the Sb only polymers. This is inkeeping with the belief that the higher the peak crystallisationtemperature on cooling from melt (Tc) the greater the opportunity fordevelopment of crystallisation in the spinline—all other conditionsbeing constant.

The results show that using the catalyst system and polyesterificationprocess of the invention it is possible to produce polymer havingproperties which are comparable with or better than polymer made using astandard antimony catalyst, whilst the level of antimony is considerablyreduced. The reduced metal burden of the polyesters of the inventionlead to a cleaner polymer which provides environmental benefits and alsoprocessing benefits in the end use. For example, a high level ofantimony catalyst can lead to levels of insoluble elemental antimony inthe finished polymer which may cause breakage of or defects in a fibremade from such polymer. Reducing the elemental antimony can thereforeproduce a better fibre and enable the fibre spinning process to beoperated at higher speeds and with superior “runnability”. Furthermore,colour management of the polymer, for example by incorporation of dyesor inorganic toners, may be easier because the greying effects ofantimony are reduced whilst the polymer is less yellow than a similarpolymer containing more titanium.

The benefits of reduced levels of antimony in the final polymer areuseful in most melt processing applications. For example in filmmanufacture the level of imperfections in the film would be expected tobe lower using polyester made according to the method of the invention.The polymer also has a better appearance; the lower levels of antimonygiving a polymer having a better “sparkle”. In bottle manufacture, theimproved melt rheological processing properties may also providebenefits in process stability and product quality. The polyester made bythe process of the invention and using the catalyst of the invention istherefore useful in producing films and rigid pacaking articles such asbottles, trays and clamshell containers.

1. A catalyst composition suitable for use as a catalyst for thepreparation of an ester comprising (a) a preformed metal-organiccompound which is the product resulting from the reaction of (i) anorthoester or condensed orthoester of titanium, zirconium, or aluminum,(ii) an alcohol containing at least two hydroxyl groups, (iii) a2-hydroxy carboxylic acid, and (iv) an organic base selected from thegroup consisting of quaternary ammonium hydroxide compounds; and (b) atleast one compound of germanium, antimony or tin.
 2. A catalystcomposition as claimed in claim 1, wherein the metal-organic compound isa reaction product of a titanium orthoester.
 3. A catalyst compositionas claimed in claim 1, wherein said alcohol is a dihydroxy alcohol.
 4. Acatalyst composition according to claim 3 wherein the metal-organiccompound comprises titanium or zirconium and contains from 2 to 12 molesof dihydroxy alcohol per mole of titanium or zirconium.
 5. A catalystcomposition as claimed in claim 1, wherein said carboxylic acid islactic acid, citric acid, malic acid or tartaric acid.
 6. A catalystcomposition according to claim 1 wherein the metal-organic compoundcomprises titanium or zirconium and contains from 1 to 4 moles of2-hydroxy carboxylic acid per mole of titanium or zirconium.
 7. Acatalyst composition as claimed in claim 1, wherein said base istetrabutyl ammonium hydroxide, tetraethylammonium hydroxide,trimethyl(2-hydroxyethyl)ammonium hydroxide, or benzyltrimethyl ammoniumhydroxide.
 8. A catalyst composition as claimed in claim 1, wherein themetal-organic compound comprises the reaction product of a titaniumorthoester, citric acid, a dihydric alcohol and an inorganic base inwhich the mole ratio of titanium:acid:dihydric alcohol: base is in therange 1:1.5-3.5:4-10:2-12.
 9. A catalyst composition according to claim1, wherein the compound of germanium is germanium dioxide or a salt ofgermanium.
 10. A catalyst composition according to claim 1, wherein thecompound of antimony is antimony trioxide or a salt of antimony.
 11. Acatalyst composition according to claim 1, wherein the compound of tinis a tin salt, a dialkyl tin oxide, a dialkyl tin dialkanoate or analkylstannoic acid.
 12. A catalyst composition according to claim 1,wherein the weight ratio of component (a) to component (b) is up to1:1000, calculated as weight of Ti, Zr or Al in component (a) to weightof Ge, Sb or Sn in component (b).
 13. A process for the production of apolyester comprising the reaction of a compound selected from the groupconsisting of terephthalic acid, dimethyl terephthalate, isophthalicacid, dimethyl isophthalate, dimethyl 2,6 naphthalate or naphthalenedicarboxylic acid with an alcohol selected from the group consisting of1,2-ethanediol, 1,4-butanediol, 1,3 propane diol, 1,6-hexanediol,trimethylol-propane and pentaerythritol in the presence of a catalystcomposition comprising: (a) a preformed metal-organic compound which isthe product resulting from the reaction of (i) an orthoester orcondensed orthoester of titanium, zirconium, or aluminum, (ii) analcohol containing at least two hydroxyl groups, (iii) a 2-hydroxycarboxylic acid, and (iv) an organic base selected from the groupconsisting of quaternary ammonium hydroxide compounds; and (b) at leastone compound of germanium, antimony or tin.
 14. A process as claimed inclaim 13 in which the esterification reaction is a direct esterificationor a transesterification and the catalyst is present in an amount in therange 0.2 to 1200 parts per million calculated as parts by weight ofmetal with respect to weight of product ester.
 15. A process as claimedin claim 13, wherein the esterification is a polyesterification and thecatalyst is present in an amount in the range 5 to 500 parts per millioncalculated as parts by weight of metal with respect to weight of productpolyester.
 16. A process for the manufacture of a polyester articlecomprising: (i) reacting together a compound selected from the groupconsisting of terephthalic acid, dimethyl terephthalate, isophthalicacid, dimethyl isophthalate, dimethyl 2,6 naphthalate and naphthalenedicarboxylic acid with an alcohol selected from the group consisting of1,2-ethanediol, 1,4-butanediol, 2,3-propanediol, 1,6-hexanediol,trimethylol-propane and pentaerythritol in the presence of a catalystcomposition comprising: (a) a preformed metal-organic compound which isthe product resulting from the reaction of an orthoester or condensedorthoester of titanium, zirconium; or aluminum, an alcohol containing atleast two hydroxyl groups, a 2-hydroxy carboxylic acid, and an organicbase selected from the group consisting of quaternary ammonium hydroxidecompounds, and (b) at least one compound of germanium, antimony and tin,(ii) optionally subjecting the resulting polymer to a solid phasepolymerisation reaction, to form a polyester material having anintrinsic viscosity of at least 0.5 dl/g, as measured by the method ofASTM D-4603, and (iii) forming said polyester article from said polymerin the melt phase and (iv) cooling.
 17. The process of claim 16 whereinsaid polyester article is a polyester fiber, and further comprising theadditional step of drawing said polyester fiber.
 18. A polyester articlecontaining residues of a catalyst composition comprising: (a) apreformed metal-organic compound which is the product resulting from thereaction of an orthoester or condensed orthoester of titanium,zirconium, or aluminum, an alcohol containing at least two hydroxylgroups, a 2-hydroxy carboxylic acid, and an organic base selected fromthe group consisting of quaternary ammonium hydroxide compounds, and (b)at least one compound of germanium, antimony or tin.
 19. A polyesterarticle as claimed in claim 18, which is a fibre, film or container. 20.A polyester article as claimed in claim 19 comprising an industrialfibre.
 21. A polyester article as claimed in claim 19 comprising a fibresuitable for use as a textile fibre.
 22. A tire cord comprising saidindustrial fiber of claim
 20. 23. A seat belt comprising said industrialfiber of claim
 20. 24. A rubber reinforced article comprising said tirecord of claim
 22. 25. A tire comprising said rubber reinforced articleof claim
 24. 26. A safety restraint system comprising said seat belt ofclaim
 23. 27. A polyester article as claimed in claim 19 comprising afilm.
 28. A polyester article as claimed in claim 19 comprising a rigidpackaging article.
 29. A process for the manufacture of a polyesterfiber comprising: (i) reacting together a compound selected from thegroup consisting of terephthalic acid, dimethyl terephthalate,isophthalic acid, dimethyl isophthalate, dimethyl 2,6 naphthalate andnaphthalene dicarboxylic acid with an alcohol selected from the groupconsisting of 1,2-ethanediol, 1,4-butanediol 2,3-propanediol,1,6-hexanediol, trimethylol-propane and pentaerythritol in the presenceof a catalyst composition comprising: a preformed metal-organic compoundwhich is the product resulting from the reaction of an orthoester orcondensed orthoester of titanium, zirconium, or aluminum, an alcoholcontaining at least two hydroxyl groups, a 2-hydroxy carboxylic acid,and an organic base selected from the group consisting of quaternaryammonium hydroxide compounds, and (ii) optionally subjecting theresulting polymer to a solid phase polymerisation reaction, to form apolyester material having an intrinsic viscosity of at least 0.5 dl/g,as measured by the method of ASTM D-4603, and (iii) forming saidpolyester fiber from said polymer in the melt phase and (iv) cooling.30. The process of claim 29 further comprising the additional step ofdrawing said polyester fibre.
 31. A polyester article according to claim28, wherein said rigid packaging article comprises a bottle.
 32. Apolyester article according to claim 28, wherein said rigid packagingarticle comprises a jar.
 33. A polyester article according to claim 28,wherein said rigid packaging article comprises a clamshell package. 34.A process according to claim 29, wherein the catalyst compositionadditionally contains at least one compound of germanium, antimony andtin.
 35. A polyester material containing residues of a catalystcomposition comprising a metal-organic compound consisting essentiallyof the product resulting from the reaction of: (a) an orthoester orcondensed orthoester of titanium, zirconium, or aluminium; (b) analcohol containing at least two hydroxyl groups; (c) a 2-hydroxycarboxylic acid; and (d) an organic base selected from the groupconsisting of tetraethyl ammonium hydroxide or benzyltrimethyl ammoniumhydroxide.
 36. A polyester material according to claim 35, wherein themetal-organic compound is a reaction product of a titanium orthoester.37. A polyester material according to claim 35, wherein said carboxylicacid is selected from lactic acid, citric acid, malic acid and tartaricacid.
 38. A polyester material according to claim 35, wherein themetal-organic compound contains from 1 to 4 moles of 2-hydroxycarboxylic acid per mole of titanium or zirconium.
 39. A catalystcomposition consisting essentially of a metal-organic compound which isthe product resulting from the reaction of: (a) an orthoester orcondensed orthoester of titanium, zirconium, or aluminium; (b) analcohol containing at least two hydroxyl groups; (c) a 2-hydroxycarboxylic acid; and (d) an organic base selected from the groupconsisting of tetraethyl ammonium hydroxide or benzyltrimethyl ammoniumhydroxide.
 40. A catalyst composition according to claim 39, wherein themetal-organic compound is a reaction product of a titanium orthoester.41. A catalyst composition according to claim 39, wherein saidcarboxylic acid is selected from lactic acid, citric acid, malic acidand tartaric acid.
 42. A catalyst composition according to claim 39,wherein the metal-organic compound contains from 1 to 4 moles of2-hydroxy carboxylic acid per mole of titanium or zirconium.
 43. Acatalyst composition according to claim 39, consisting essentially of ametal-organic compound which is the product resulting from the reactionof: (a) an orthoester or condensed orthoester of titanium or zirconium;(b) a dihydric alcohol; (c) a 2-hydroxy carboxylic acid selected fromthe group consisting of lactic acid, citric acid, malic acid andtartaric acid; and (d) an organic base selected from the groupconsisting of tetraethylammonium hydroxide, or benzyltrimethyl ammoniumhydroxide.
 44. The polyester material of claim 35, wherein the polyestermaterial is in the form of a fiber.
 45. The fiber of claim 44, whereinthe fiber has improved extensional viscosity.
 46. The polyester fiber ofclaim 44 wherein said fiber is an industrial fiber.
 47. The polyesterfiber of claim 44 wherein said fiber is a textile fiber.
 48. A tire cordcomprising said industrial fiber of claim
 46. 49. A seat belt comprisingsaid industrial fiber of claim
 46. 50. A rubber reinforced articlecomprising said tire cord of claim
 48. 51. A tire comprising said rubberreinforced article of claim
 50. 52. A safety restraint system comprisingsaid seat belt of claim
 49. 53. The fiber of claim 45 wherein said fiberis industrial fiber.
 54. The fiber of claim 45 wherein said fiber is atextile fiber.
 55. A polyester fiber according to claim 44, wherein thecatalyst composition additionally contains at least one compound ofgermanium, antimony and tin.
 56. A catalyst composition consisting of ametal-organic compound which is the product resulting from the reactionof: (a) an orthoester or condensed orthoester of titanium, zirconium, oraluminium; (b) an alcohol containing at least two hydroxyl groups; (c) a2-hydroxy carboxylic acid; and (d) an organic base selected from thegroup consisting of tetraethyl ammonium hydroxide or benzyltrimethylammonium hydroxide.